The MDPE system is designed for coldwater applications only.
You will first need to insert the pipe liner into the pipe (this might be a tight fit and may require a hammer to tap it in gently).
You will then need to loosen the nut on the fitting and push the pipe in as far as it can go and then tighten the nut back up on the fitting.
The MDPE fittings have been tested to 16 bars and the pipe has been tested to 12 bars.
No hot water should be passed through the system as it is designed for cold water only.
If possible then the system should be installed away from any hot pipe work as it will start to affect the performance of the system with temperatures as little as 30°c.
No, there is no need to protect the system. It will just sit in place under the flooring of the house.
If installed externally it should be lagged to protect it from frost and ultra violet degradation.